BY HEAT OF WATEE -AND MEKCUEY. 



245 



The coeiRcient of expansion of this sort of glass was determined by weigh- 

 ing a piece of the same tubing in water at low and high temperatures. The 

 tube was drawn out and fused as shown in the annexed figure ; but before 

 sealing to, a small piece of lead was placed in the tube to cause it to sink in 

 water. It was weighed in water with the following results: — 



The values in the third column are deduced by multiplying the obser\-ed loss of weight 

 in water by the volume occupied by water (1-^at) at the temperature at which the 

 weighing was made (Table X.); for if the weights of water displaced be reduced to 4°, 

 the numbers so obtained will express in cubic centimetres the volumes of glass at different 

 temperatures. 



The coefficient of expansion of the glass between ll°-7 and 95°'20 equals from the 

 above values 0-002143, taking its volume at 11°"7=1, 

 or 0-002566 between 0° and 100°, taking its volume at 0°=1, 



or the formula for the cori'ection of the expansion of this sort of glass will be 



V,=V„(1 +0-00002566^). 



In carrying out the experiments with mercury, the bucket was first weighed in air, 

 then placed in the silver cylinder and boiled in the water for about half an hour to free 

 it from air ; the mercury during the time being dried, as already mentioned, and still hot, 

 was poured into the bucket, just lifted out, but quite full of water. In this manner it 

 was possible to fill the bucket with mercury without air getting between it and the glass. 

 After filling the bucket, the boiling was continued for a quarter of an hour, and then 

 the observation made in the ordinary manner. Table XII. contains the five series made 

 with different specimens of mercury used. To find the weight of the mercury after 

 the weighings had been made, it was emptied into a crucible, dried on a water-bath, 

 and weighed. 



